Having just re-read Arthur C. Clarke’s The City and the Stars for the first time in a couple of decades, I’ve been preoccupied by the idea of ‘deep time,’ and astronomical events that play out over billions of years. The fictional trick, of course, is to pair human observation with events that take aeons to unfold. In Clarke’s novel, the city of Diaspar is a place that is almost outside of time, a self-contained and beautiful place whose very inwardness ultimately becomes stultifying. But the vision of this glowing jewel of a city surviving amidst the dunes of an ancient Earth is one of those science fiction images that stick with you over a lifetime of reading.

New work out of Vanderbilt University now suggests other deep time images, but they’re likely to be more fantasy than science fiction. Imagine a star moving fast enough to escape the galaxy, living out its life on a long trajectory that will take it into intergalactic space. Kelly Holley-Bockelmann and Lauren Palladino think they can identify more than 675 stars moving out of the Milky Way that have been ejected from the galactic core, red giants with high metallicity — a large proportion of chemical elements other than hydrogen and helium — that are presumably the result of close encounters with the supermassive black hole at the center of the galaxy.

Moving at something like 900 kilometers per second, a hypervelocity star of the kind catalogued by Holley-Bockelmann and Palladino takes roughly 10 million years to travel from the galactic hub to the outer edge of the spiral. Pushing out into the intergalactic dark, it would go through normal stellar evolution that takes it to the red giant stage, having begun as a small star relatively like our Sun. So could planets exist around such a star? If so, any civilization that might emerge on them would play out its lifetime well beyond the vast city of stars that is the Milky Way.

Image: A supermassive black hole at galactic center may be responsible for hypervelocity stars that are leaving the galaxy at high speeds. Credit: NASA/JPL.

That would make for some interesting tales, and science fiction stories like Poul Anderson’s World Without Stars (1966) explore the experience of extraterrestrials living in a system outside the galaxy. But planets would be seriously problematic among hypervelocity stars, given that the scenario under investigation involves a young binary system that wanders too close to the four-million solar mass black hole at the hub. While one star spirals in toward the black hole, the other would be flung outward, presumably disrupting any nascent planetary system around it.

Another mechanism involves a single star making too close a pass when the central black hole is ingesting a smaller black hole. Both situations produce the hypervelocity kick that propels a star out of its galaxy. That’s quite a lot to ask for the stability of any planetary system.

Working with Sloan Digital Sky Survey data, the Vanderbilt work probes these mechanisms, beginning with what has been called a ‘field of streams’ that extends out to about 100 kiloparsecs from the Milky Way. A similar stream extends outward from M31, the Andromeda Galaxy. Given that our two galaxies are not (yet) interacting, the black hole scenarios make a better explanation for these streams of stars than interactions between galaxies. To become intergalactic wanderers, stars must exceed the Milky Way’s escape velocity, now pegged at somewhere between 500 and 600 kilometers per second. So we have a mixture of bound stars on highly eccentric orbits and hypervelocity stars that are escaping from the galaxy altogether.

Stars on their way out of the Milky Way should show a definite signature. From the paper:

It is useful to compare this to theoretical predictions of stellar ejections from the Milky Way (Kollmeier et al. 2009). Stars ejected from the galaxy center through three-body interactions with a SMBH [supermassive black hole] will typically have much higher metallicity than stars that were stripped from satellite galaxies originating in the outskirts of a galaxy halo…

Or as Holley-Bockelmann puts it in this Vanderbilt news release:

“These stars really stand out. They are red giant stars with high metallicity which gives them an unusual color.”

Usefully, stars between galaxies may offer up insights into the history and evolution of galaxy clusters, but followup observations are needed to weed out any candidates that are actually much closer brown dwarfs rather than hypervelocity red giants. As to my musings about planetary systems around hypervelocity stars, they’re likely to be little more than that, because how a planetary system could stay gravitationally bound to a star that has had a violent encounter with a black hole remains a mystery — most likely any previously existing planets would be torn away to become lone wanderers themselves. But if anyone has seen any work on planetary survival in these scenarios, please let me know. It seems a wild stretch.

The paper is Palladino et al., “Identifying High Metallicity M Giants at Intragroup Distances with SDSS,” accepted for publication in The Astronomical Journal Vol. 143, No. 6 (May, 2012), p. 128 (abstract / preprint). Another science fictional treatment of stars outside galaxies is Iain Banks’ Against a Dark Background (1993), which is finally nearing the top of my reading stack.

This article was originally posted on Centauri Dreams

One of the topics receiving fairly little coverage in the excitement of the Planetary Resources announcement is asteroid deflection. It seems clear that learning how to reach an asteroid and extract everything from water to platinum-group metals from it will also teach us strategies for changing an asteroid’s trajectory, in the event we find one likely to hit the Earth. The recent report from the Keck Institute of Space Studies makes this point clearly in the context of its own mission study, a plan to retrieve a small (7 m) asteroid and park it in lunar orbit.

What Asteroid Operations Can Teach Us

Although Planetary Resources estimates there are more than 1500 asteroids that are as easy to get to as the Moon, we still have a long way to go in understanding basic facts about these objects and their composition. Take dust, which will probably vary from object to object, but which could cause problems for ‘gravity tractor’ concepts where a spacecraft is used to deflect an asteroid without physically contacting it. If the rendezvous with the asteroid can be managed far enough from Earth, the gravitational field of a nearby orbiting body as tiny as a spacecraft can, over a period of years or even decades, bring about the needed course change.

But assuming your vehicle works with the kind of solar electric propulsion envisioned by the Keck study, dust could be a factor if the engine exhaust reaches the asteroid as part of needed station-keeping (this is perhaps an argument for solar sail technologies in these scenarios). What seems to be a small issue becomes a big unknown when you think about the multi-year presence of a gravity tractor spacecraft around such an asteroid. Direct study, as via Planetary Resources robotic technologies or manned crews examining a captured asteroid in lunar orbit, should help us learn more about how dust is moved and settles on an asteroid surface.

Other factors listed by the Keck report:

Anchoring: We need to acquire the ability to land a robotic spacecraft on an asteroid and anchor it there, a challenge any mining venture will have to resolve.

Structural characterization: This is a big one. We need to understand an asteroid from the inside out, since a prime deflection method is to hit the asteroid with enough of a blow to change its course. But we know little about what happens to an asteroid when this occurs because ejecta from the impact could multiply the momentum given to the NEA by the impactor.

Proximity operations: How do we dock with the asteroid and navigate near it? We’ll learn many of these things through actual robotic asteroid operations, and as we saw last time, having a small asteroid available for examination in lunar orbit would far surpass the 60 grams of surface material we’re going to have returned from the upcoming OSIRIS-REx mission.

These are all technical matters, but it goes without saying that a successful asteroid retrieval of the kind Keck envisions would also draw public attention to the asteroid defense element of all our studies of near-Earth objects. And in addition to its uses in providing unique, space-based resources for radiation shielding and propellant extraction, an asteroid retrieval would offer up some of the options we may someday want to use in space elevators. Says the report:

One day, in the more distant future, it is possible that a small NEA (~10 m) returned to E-M L2/L1 could act as an orbiting platform/counter weight for a lunar space elevator to allow routine access to and from the lunar surface and also function as a space resource processing facility for mining significant quantities of materials for future human space exploration and settlement and possible return and inclusion in terrestrial markets.

Eye on an Exoplanet

The asteroid mining and retrieval idea seems so loaded with possibilities that the Keck Institute’s 51 page report can barely contain them all, but I want to close with the idea NextBigFuture has been discussing recently. Planetary Resources makes a point about the Arkyd Series 100 space telescopes it intends to begin launching as soon as 24 months from now. These are intended to begin with studies in low Earth orbit but the Arkyd Series 200 that follows would contain a propulsion system so that missions directly to new asteroid targets will become possible.

We get the same kind of look at an asteroid, says Planetary Resources, as we got when exploring the Moon with the Ranger missions (1961-65) or the Deep Impact mission at Comet 9P/Tempel in 2005. The name of the game is data acquisition as we try to decide which near-Earth asteroids are the best candidates for future operations. NextBigFuture took a look at all those telescopes — Planetary Resources describes them as “the first private space telescope… simple enough to be designed, manufactured, tested and integrated by a small team, yet robust enough to get the job done.” Could they be massed for deep space studies?

The principle is interferometry, which would allow the creation of huge telescopes, mixing signals from a cluster of small instruments to achieve high-resolutions unavailable from a single, monolithic lens. The idea has been thoroughly vetted, and with great success, with Earth-bound instruments, but French astronomer Antoine Émile Henry Labeyrie (Collège de France) has been studying what he calls a ‘hypertelescope,’ which would involve huge numbers of free-flying spacecraft combining their data to produce images that could show surface detail on exoplanets.

Labeyrie’s presentation on the topic at a European Space Agency meeting in 2009 describes a “laser-driven hypertelescope flotilla at L2” that could image continents and oceans on a world 10 light years away. These would be telescopes whose mirrors were placed kilometers apart, each of them small instruments but forming what he has called a ‘sparse giant mirror.’ Here’s the image from Labeyrie’s talk that NextBigFuture also ran. Note the resolution shown for Earth at the 10 light year distance, and the swarm of spacecraft that have been used to produce it.

In a 1996 paper, Labeyrie had this to say about interferometry and exoplanets:

As the technical difficulties will become mastered, a continuous evolution towards larger sizes is to be expected. Jupiter-like planets at 5 pc can be imaged from Earth with 10 km arrays, while Earth-like planets at 5 pc require 100 km arrays, preferably installed in space. Because such images can also yield spectra for each of their resolved elements, they should provide a better diagnostic for the presence of life, and possibly civilisation, than would spectra of unresolved planets. Other objects such as pulsars, galactic nuclei and QSOs [quasi-stellar objects] are also candidates for high resolution imaging.

Labeyrie went on to develop the concept he calls Exo-Earth Imager, one that made an appearance in New Scientist in 2006 in an article by Govert Schilling:

Labeyrie’s design for a hypertelescope takes dilute optics to the extreme. Ultimately his Exo-Earth Imager will consist of at least 150 mirror elements, each measuring 3 metres across, and spread out over an area of about 8000 square kilometres. Together, they would fly in formation around the sun to make a hypertelescope with a diameter of 100 kilometres – large enough to pick out clouds and continents on a distant relative of our home planet.

Whether or not Planetary Resources would eventually wind up creating a hypertelescope flotilla anything like this as an offshoot of its asteroid mining effort remains to be seen, but what is exciting here is the prospect of lower-cost space telescopes whose very presence may spur refinements in interferometric techniques. The same network could boost the effort to exploit sunshade concepts, in which the light of the central star is effectively nulled and the faint light of exoplanets made visible. All in all, an effort to reach and take advantage of asteroid resources could have large ramifications indeed, not all of them confined to our own Solar System.

Two papers by Antoine Labeyrie are relevant here. They are “Resolved imaging of extra-solar planets with future 10-100km optical interferometric arrays,” Astronomy and Astrophysics Supplement, v.118 (1996) p.517-524 (abstract) and “Snapshots of Alien Worlds: The Future of Interferometry,” Science 285 (1999), pp. 1864-65 (abstract). The Schilling article is “The hypertelescope: a zoom with a view,” New Scientist 23 February 2006.

This article was originally posted on Centauri Dreams

On the Trail of the Space Pirates was a 1953 adventure written by Carey Rockwell, a house pseudonym used by a Grosset & Dunlop writer who may or may not have been one Joseph Greene, an editor for the firm in that era. We don’t know for sure who ‘Carey Rockwell’ was and no one has come forward to claim the title, but see the Tom Corbett Space Cadet website for another possible clue to authorship. In any case, On the Trail of the Space Pirates took readers such as my grade school self out into the asteroid belt, where all manner of adventures occur and uranium prospectors ply their trade harassed by evil doers. The asteroids became a lively analogue to the American wild west.

Asteroid mining and the culture it spawns has a robust history in science fiction, but I couldn’t help recalling this particular book when I read about Planetary Resources and its ambitious plan to mine asteroids. The company’s intentions don’t extend all the way to the main belt, but focus on asteroids much closer to home, of which there are plenty, and out of which some 1500 may prove to be of high interest if mining is the intention. What caught me up in the spirit of the science fictional ‘belters’ was this pitch on the Planetary Resources website encouraging people to work for the company. It’s titled ‘We’re looking for a few good asteroid miners’:

1. We are finding a new way to explore space beyond Earth orbit.
2. We are a growing business with incredible people who are dedicated to Planetary Resources’ long-term objectives.
3. Like all small businesses, we are a family. We love our team and what we do.
4. You will get your hands dirty. If you prefer your hands clean, go somewhere else.
5. We have a grill. We are not afraid to use it.
6. Seattle, Washington. Ok, so it rains. It’s gorgeous, and anyone who says otherwise is from California.
7. Bottom line – we build spaceships and explore asteroids. If you need any other motivation to apply, don’t bother.

The brash spirit of those comments is a nice tonic in an era when government space programs seem rudderless and strapped for cash. Whether Planetary Resources can deliver on its promise to study and then mine iron, nickel, gold, platinum and water resources on nearby chunks of rock remains to be seen, though the list of backers — Ross Perot Jr., son of the former presidential candidate, Eric Schmidt and Larry Page of Google, movie mogul James Cameron, X Prize founder Peter Diamandis — offers hope and plenty of cash. And let’s not forget Eric Anderson (Space Adventures) and the well-traveled Charles Simonyi, who is unusual among space tourists in having made not one but two flights to the International Space Station.

This is a genuinely exciting startup that is going to teach us a lot about how fast and how soon we can develop resources in nearby space that can help us go much further afield. In Centauri Dreams terms, I always think about building the needed infrastructure in the Solar System that can one day support an interstellar effort. Extracting water that does not need to be boosted into Earth orbit and creating rocket fuel from space resources to supply future missions fits that bill, as does the hope that enough money can be turned from the extraction of precious metals to make the venture self-sustaining and prosperous. Good fortune to Planetary Resources!

The context in which this new company moves is suggested by a recent report from Caltech’s Keck Institute for Space Studies which was released in early April, and which was invariably mentioned in news reports in tandem with the Space Resources news conference on the 24th. I want to start digging into this report in the next day or two because although it focuses specifically on retrieving an asteroid, it has obvious implications not only in terms of how we might exploit its resources but learn to manipulate its trajectory. All that, of course, takes us into the realm of asteroid threat mitigation. If we one day find an asteroid that is moving on a dangerous trajectory, will we have the time and the know-how to actually do something about it?

Here it’s worth noting that the Apollo missions were able to return 382 kilograms of lunar materials over the course of their six lander missions, while NASA’s OSIRIS-REx mission is slated to retrieve about 60 grams from the asteroid known as 1999 RQ36, which orbits the Sun every 1.2 years and crosses the Earth’s orbit every September. 60 grams isn’t much, but neither is the Apollo sample return when compared to the ~500,000 kilograms of asteroid material the Keck Institute study talks about, an entire asteroid delivered to high lunar orbit by around 2025.

Can it be done? Even more significantly, can it be done without endangering the home planet? I’ll be looking further into the report tomorrow. Meanwhile, have a look at Alan Boyle’s excellent discussion of Planetary Resources’ prospects and the problems they’ll encounter along the way. And check NextBigFuture’s challenging look at a different way to use those small, inexpensive telescopes Planetary Resources intends to put into space as part of the infrastructure for studying asteroid targets. They could conceivably be used as the basis for a ‘hypertelescope,’ an interferometer with a 16,000 kilometer baseline. The possibilities for a close-up look at an exoplanet are intriguing, to say the least, and we’ll discuss them further in coming days.

I’ve believed for a long time that planetary defense demanded we develop the technologies that would get us into the outer Solar System, and we may be seeing the first steps in that process now. The painstaking study of nearby asteroids that the Planetary Resources concept will demand should pay dividends if we ever have to move one not just for resources but for safety.

This article was originally posted on Centauri Dreams

Long before Planetary Resources was a gleam in the eye of its founders, John Lewis (University of Arizona) wrote a book that put asteroid mining into the public consciousness. Mining the Sky: Untold Riches from the Asteroids, Comets and Planets (Perseus Books, 1996) contains no shortage of wonders, as in the well publicized idea that a single one-kilometer asteroid could produce enough gold and silver to equal world production for a century. David Brin writes about this on George Dvorsky’s Sentient Developments site, noting that while that would produce a collapse in gold and silver prices, it would also produce incalculable benefits in terms of raw materials production that could change the economic paradigm entirely.

Lewis is a natural fit with Planetary Resources, the highly buzzed-about startup that plans to make asteroid mining a reality, and it’s no surprise to see that he serves as one of its advisors. But remembering Mining the Sky, I was startled to discover that the idea of using asteroid resources goes all the way back to Konstantin Tsiolkovskii, who wrote about it in The Exploration of Cosmic Space by Means of Reaction Motors in 1903 — it was in this same work that the Russian rocket scientist and visionary first proposed multistage rockets using liquid hydrogen and liquid oxygen for space exploration. It seems fitting that there is an asteroid with a Tsiolkovskii connection, the object 1590 Tsiolkovskaja being named for his wife.

Image: An artist’s concept of a fragmented asteroid laden with resources. Image: NASA/JPL-Caltech/Handout , Reuters files.

A New Study on Asteroid Retrieval

Caltech’s Keck Institute for Space Studies has examined asteroid possibilities in the just released Asteroid Retrieval Feasibility Study, whose April 12 appearance was timed to perfection by the powers behind Planetary Resources. What the Keck study is interested in is returning an object not to low-Earth orbit but a high lunar orbit, allowing the project to be conducted with far more relaxed propulsion constraints than would be applied deep in Earth’s gravity well. A corollary to this is the fact that larger asteroids can be captured. The study authors settled on an asteroid 7 meters in diameter with a mass on the order of 500,000 kg. This was a 6-month study enlisting a wide range of space-minded talent (see the contributor list on p. 6 of the report).

The Keck report meshes with NASA’s current goals of sending a manned expedition to a near-Earth asteroid halfway into the next decade, though given the mutable nature of NASA’s funding, that’s the least of the reasons to make this happen. Even so, an asteroid retrieval has definite consequences for manned flight. What Keck has in mind is robotic, unmanned missions that culminate in a scout mission, also robotic, to enable detailed mission planning. The full retrieval mission is seen as a precursor to subsequent human missions to this and other NEAs. An NEA in high-lunar orbit then becomes an obvious and accessible target for astronaut visitation.

Again, no astronauts on the retrieval mission, which is robotic. But:

Taken together, these attributes of an ACR [Asteroid Capture and Return] mission would endow NASA (and its partners) with a new demonstrated capability in deep space that hasn’t been seen since Apollo. Once astronaut visits to the captured object begin, NASA would be putting human explorers in contact with an ancient, scientifically intriguing, and economically valuable body beyond the Moon, an achievement that would compare very favorably to any attempts to repeat the Apollo lunar landings.

Reasons for Snatching an Asteroid

Why retrieve an asteroid in the first place? Here’s a distilled rational from the executive summary, one that begins with a focus on the effect of spurring manned spaceflight:

It would provide a high-value target in cislunar space that would require a human presence to take full advantage of this new resource. It would offer an affordable path to providing operational experience with astronauts working around and with a NEA that could feed forward to much longer duration human missions to larger NEAs in deep space. It would provide an affordable path to meeting the nation’s goal of sending astronauts to a near-Earth object by 2025. It represents a new synergy between robotic and human missions in which robotic spacecraft retrieve significant quantities of valuable resources for exploitation by astronaut crews to enable human exploration farther out into the solar system.

All true, of course, but it’s only after this spadework has been done that the report turns to what has electrified the space community about Planetary Resources and its own asteroid plans, and it’s nothing like an Apollo-style effort to get people to particular destinations. The goal is broader and much longer-lasting. Once we have an asteroid, either by traveling to it or by inducing it into a lunar orbit for further exploitation, we have the ability to extract materials from it. All this gets into the real infrastructure-building components of asteroid mining:

…water or other material extracted from a returned, volatile-rich NEA could be used to provide affordable shielding against galactic cosmic rays. The extracted water could also be used for propellant to transport the shielded habitat. These activities could jump-start an entire in situ resource utilization (ISRU) industry. The availability of a multi-hundred-ton asteroid in lunar orbit could also stimulate the expansion of international cooperation in space as agencies work together to determine how to sample and process this raw material. The capture, transportation, examination, and dissection of an entire NEA would provide valuable information for planetary defense activities that may someday have to deflect a much larger near-Earth object. Finally, placing a NEA in lunar orbit would provide a new capability for human exploration not seen since Apollo.

Aspects of the Retrieval Mission

Two aspects of the asteroid retrieval campaign are immediately obvious. Before retrieving anything, we need an extended effort to identify objects that fit the bill physically and offer up orbital parameters that would make them good candidates for the return mission. We also need a transportation method, and here what the Keck study advocates is a ~40-kW solar electric propulsion system with a specific impulse of 3,000 seconds. It’s interesting to see by the report’s figures that, given a single launch to low-Earth orbit aboard an Atlas V-class vehicle, the ultimate plan would be to retrieve 28 times the mass launched to LEO and bring it into high lunar orbit.

The mission plan is fascinating and fodder for science fiction writers. The solar electric propulsion system would be used to spiral the vehicle into high-Earth orbit and a lunar gravity assist would then put the vehicle on a trajectory to the NEA. The report allocates 90 days for studying the NEA and capturing and ‘de-tumbling’ the asteroid, transporting it back to the Earth-Moon system for a second lunar gravity assist that would be used to capture it. Transfer to a stable high lunar orbit would take place about 4.5 months after the first gravity assist.

All of this presupposes mechanisms for stabilizing and moving the asteroid, which the report says could be done with a high-strength bag assembly, deployable and inflatable arms and cinching cables, the bag being 10 meters by 15-meters in diameter looking like this:

Image: The capture mechanism deployed and in operation. Credit: Rick Sternbach/KISS.

But before any such mission can be flown, we also need improved ways of studying potential targets. Planetary Resources has the idea of launching inexpensive telescopes that could sample a wide variety of NEAs, while the Keck report notes the value of the solar electric propulsion system for sending multiple-target robotic precursors that would precede any human missions. As opposed to the upcoming (2016) OSIRIS REx mission, which will return 60 grams of surface material, a robotic precursor like this would be used to bring back large boulders and regolith samples from any human targets prior to sending manned crews there.

The report’s focus on resource acquisition in space is heartening. Check this:

The asteroidal material delivered to cislunar space could be used to provide radiation shielding for future deep space missions and also validate in-situ resource utilization (ISRU) processes (water extraction, propellant production, etc.) that could significantly reduce the mass and propulsion requirements for a human mission. The introduction of ISRU into human mission designs could be extremely beneficial, but until the processing and storage techniques have been sufficiently tested in a relevant environment it is difficult to baseline the use of ISRU into the human mission architecture. Bringing back large quantities of asteroid materials to an advantageous location would make validation of an ISRU system significantly easier.

Well said — the whole notion of in situ acquisition and utilization is critical as we look toward building a true human future in space. Part of the Planetary Resources plan is to extract water from asteroids not only for human needs (much better than launching from deep within the gravity well) but also for the creation of rocket fuel. The report’s emphasis on the need to bring back asteroid materials to study the prospects in detail is wise, because we need to learn how effectively we can go about extracting these materials and turning them around for space use.

But there are other areas where moving into the asteroids, first with robots and then human crews, makes abundant sense. Tomorrow I want to examine asteroid deflection as one major area that will benefit from these activities, and we’ll also look at the ramifications of all those telescopes Planetary Resources plans to put into space. We may only be scratching the surface of how useful our future ability to move tools and crews to asteroids — or to move asteroids themselves — may turn out to be in building the next phase of human civilization.

This article was originally posted on Centauri Dreams

by Larry Klaes

Larry Klaes is a long-time Centauri Dreams contributor, a practitioner of the Tau Zero Foundation and a serious devotee of space exploration and its history. Here he gives us a look at the Pioneer probes that first took us to the outer Solar System, journeys that foreshadowed the later exploits of the Voyagers and the more recent New Horizons mission to Pluto/Charon. It’s hard to believe that it’s been fully forty years since the Pioneers were launched. They came out of the era when thinking big was the order of the day, Apollo was putting astronauts on the Moon and human expansion into the cosmos seemed inevitable. When we ponder today’s budget shortfalls and drifting public attention, it’s heartening to recall that era even as we speculate about missions that will follow up on the findings of these two remarkable probes.

The early 1970s was an exciting time for lunar and planetary exploration. On the Moon, Apollo was still placing pairs of astronauts on Earth’s natural satellite to collect hundreds of pounds of lunar surface material and other priceless data. The Soviet Union was conducting a quite successful automated survey of the Moon with their two Lunakhod rovers and returning small but still valuable samples with their Luna series of landers.

The United States Mariner 9 and the Soviet Mars 2 and 3 probes were circling the Red Planet, returning the first in-depth images and data about that world which showed that Mars was not the dead and merely cratered realm that earlier flyby missions with their limited coverage had led scientists to believe. There was also excitement about an upcoming mission named Viking to place two robot landers on Mars to search for life there.

Closer to the Sun, the Soviets had finally succeeded in landing intact and functioning on the hellish world of Venus with their Venera probes. America was preparing a probe named Mariner 10 that would not only flyby Venus and return the first close-up images of its thick and cloudy atmosphere, but proceed on to Mercury and reveal what that little world really looked like.

The outer solar system had not been neglected in NASA’s plans for deep space exploration. The agency was preparing a modified version of its original Grand Tour plan, which would have sent two nuclear-powered probes past every world from Jupiter to Pluto in the summer of 1977.

No human vessel had ever visited the celestial realm where the gas giant planets dominated, or even crossed the Planetoid Belt which lay between the small and rocky terrestrial worlds of the inner solar system and the Jovian behemoths. Space engineers and officials realized they needed a precursor mission to pave the way for the success of these later more sophisticated machines. Two aptly named craft called Pioneer – coming from a long line of automated explorers going back to the earliest days of the Space Age – were designed and built for this task.

Image: Launch of Pioneer 10. Credit: NASA.

Pioneer F and G, which would receive the respective numbers 10 and 11 once they had been successfully launched on their missions, were hardy little vessels dominated by large parabolic high-gain radio dish antenna for communicating with an Earth that would eventually be hundreds of millions of miles away. Their computer “brains” were quite simple as dictated by the technology of the day, the size of the probes, and their working environment. Pioneer 10 and 11 would be kept functioning for at least several years by four RTGs attached to long booms on the probes, necessitated by the decreasing radiant energy of the distant Sun. Eleven scientific instruments were chosen for the mission.

Pioneers’ primary tasks were to do a Jupiter flyby and return images and data on the planet’s atmosphere while also attempting to glean clues about its deep and mysterious interior. Unlike the terrestrial worlds, which generally consist of a relatively thin layer of air over a rocky crust which in turn covered layers of molten and solid iron along with other minerals, the Jovian globes were primarily all atmosphere, though it was speculated that as one descended towards Jupiter’s core, the incredible pressures created some very strange physics with the surrounding gases. In any case, there was no actual surface such as human beings were accustomed to on Earth.

The Pioneers would also examine in situ the vast Jovian magnetosphere, whose intense cracklings could be picked up by radio astronomers on Earth and was presumed to be home to very lethal amounts of radiation. Project team members would even try to image and refine the masses of some of Jupiter’s four Galilean moons if possible. Although known to humanity since at least 1610, the worlds of Io, Europa, Ganymede, and Callisto were little better than points of light with a few indistinct smudges seen on them after almost four centuries of telescopic examination by astronomers.

When the time came for Pioneer 10 and 11 to make their daring plunges past Jupiter, an interesting consequence would happen: The massive bulk of that alien world combined with their already high rates of acceleration would create for the little explorers what is known as a slingshot effect. The Pioneers would be given just enough kinetic energy from Jupiter to eventually escape the gravitational pull of the whole Sol system and become the first human-made objects to enter interstellar space. In a sense, Pioneer 10 and 11 would become our species first representatives in the Milky Way.

The Pioneer team and NASA Ames acknowledged this fact but made no particularly lavish public note about this rather remarkable landmark in space history. After all, the probes were not expected to last in terms of returning data much after their Jovian encounters. Even though they were the fastest vessels yet sent by humanity into space, they were not aimed at any particular star and would still take tens of thousands of years just to reach the distance to the nearest system, Alpha Centauri. Besides, in a galaxy composed of roughly 400 billion star systems over 100,000 light years across, what were the chances that anyone would ever be able to find or notice two inert specks of metal and wiring drifting aimlessly through deep space?

“A Special Message from Mankind”

In 1971, a group of science correspondents from the national press were invited by NASA to visit TRW Systems in California, where Pioneer 10 was undergoing tests in a giant simulator which reproduced the harsh conditions that both of the robot explorers would encounter beyond Earth.

One of the reporters present that day had an epiphany about the Pioneers’ post-Jupiter mission as he looked at the silvery probe through the simulator portholes. To quote from the Epilog of the official NASA Publication on the probes, Pioneer Odyssey (SP-396, Revised Edition, 1977):

“Eric Burgess, then with The Christian Science Monitor, visualized the passage of Pioneer 10 beyond the Solar System as mankind’s first emissary to the stars. This spacecraft should carry a special message from mankind, he thought, a message that would tell any finder of the spacecraft a million or even a billion years hence that planet Earth had evolved an intelligent species that could think beyond its own time and beyond its own Solar System.”

Burgess presented his idea to two fellow correspondents, Don Bane and Richard Hoagland (yes, *that* Richard Hoagland), who “enthusiastically agreed” with Burgess. They in turn sought out a scientist named Carl Sagan, who was at the nearby Jet Propulsion Laboratory (JPL) in Pasadena involved with the Mariner 9 mission to Mars.

A longtime advocate of extraterrestrial life, Sagan was as enthusiastic about this message to ETI as the correspondents were. Upon requesting and receiving permission (somewhat surprisingly) from NASA to go ahead with this plan, Sagan and his colleague at Cornell University, Dr. Frank Drake of SETI Project Ozma fame, put together a message on a golden plaque that was small only in its relative physical size. Everything else about what would become known as the Pioneer Plaque was as large and as vast as its potential ramifications for humanity’s future expansion into the Cosmos.

At six by nine inches in diameter and just 0.050 inch thick, the Pioneer Plaque was similar in size to a very thin hardcover book. Unlike the vast majority of terrestrial books, however, this one could not be inscribed with any standard human language, for its intended recipients were not expected to know any Earthly tongue or even its planet of origin. Instead, the plaque designers would use the hopefully universal language of science. After all, the Pioneer probes would only be found by someone with the capability for interstellar travel, as the probes will probably never pass through any star systems in the Milky Way galaxy during their incredibly long celestial journeys.

The messages on the plaque were direct and confined in quantity: To explain the purpose of the probes’ mission, to show where they came from, and who built and launched them into the galactic neighborhood.

The mission purpose was depicted by a basic diagram of our Sol system from our yellow dwarf star to Pluto (the first members of the Kuiper Belt after Pluto would not be discovered until 1992). Saturn got a thin line to represent its impressive ring system: The less prominent rings of the three other Jovian worlds had yet to be known. Using an arrow-tipped line, the Pioneer probe was shown moving from the third small circle (Earth) to between and past Jupiter and Saturn, its antenna pointing back at its place of origin. The various sizes of the planets in our Sol system were stated in binary notation.

So that the recipients could have a chance at understanding the measurements on the plaque, Sagan and Drake made a small representation of the “hyperfine transition of neutral atomic hydrogen.” With hydrogen being the most abundant element throughout the Universe, the engraved image allows the finders of the plaque a way to comprehend both time and physical length.

Between the hydrogen atom and the Sol system depictions was a radial pattern of fifteen lines with binary tick marks on them. These are the distances and rotation rates of pulsars, rapidly rotating neutron stars that have been called galactic beacons by some astronomers. The plaque creators felt that, working with the limited canvas they had along with where and how the probes will most likely be found, this was the best way to show those who come upon the Pioneer probes where their makers came from both in space and time, as the spinning rates of pulsars do slow down.

“The Most Mysterious Part of the Message”

Of all the items to be engraved on the Pioneer Plaque, nothing would draw the most attention and commentary as the two human figures representing our species to the presumed recipients. Drawn by artist Linda Salzman Sagan, who also happened to be Carl’s second wife at the time, the human male and female were considered by Sagan to be “the most mysterious part of the message” as he wrote about them in his 1973 book The Cosmic Connection: An Extraterrestrial Perspective. It was thought that whoever found the Pioneers would not only have to be more advanced than their makers, but also bear little resemblance to our species, as the future discoverers were presumed to originate from and evolve in the seas of another and quite different world from ours.

Of course it was also possible – and in fact rather more likely by comparison – that one or both of the Pioneer probes might be recovered not by an ETI but by the descendants of humanity from Earth, who may find themselves spread throughout the Milky Way galaxy in distant epochs. Certainly some of our future children might be interested in recovering a rare relic from among the earliest days of humanity’s Space Age, which has been estimated to remain intact for at least one billion years in interstellar space.

It is also conceivable that the human descendants who could find the Pioneers may no longer resemble the men and women who built and launched the probes way back in the late Twentieth Century, having undergone biological and technological changes through genetic engineering to suit such situations as adaptation to alien environments and cultural aesthetics. There is also the possibility that the terran intelligences which finally enter the wider galaxy may have come solely from our technological developments, in which case they would bear almost no resemblance to their creators at all.

If nothing else, the Pioneers and their plaques certainly deserve a better fate than the one given in the sub-par 1989 film Star Trek V: The Final Frontier, where a Klingon warship comes upon the long-inactive Pioneer 10 tumbling through the inky void. The ship’s commander considers the Earth probe to be little more than space junk and uses the relic for some target practice, subsequently turning it and the plaque into little pieces of metal.

The two figures on the Pioneer plaque were drawn to be “pan-racial”; this meant that the artist tried to incorporate the physical features of three of the major human races onto her creations. Both were rendered without any clothing and with the male raising his right arm in what would hopefully be interpreted as a form of friendly greeting. To give the recipients an idea as to how big Pioneer’s builders were, a schematic representation of the probe was placed behind the humans, along with a binary mark on the far right to further indicate the height of the woman.

As Sagan would document in The Cosmic Connection, the reactions to the plaque and especially the nude human representations from the bipedal inhabitants of the third planet from Sol were wide, varied, and anything but tepid. While many responses were very positive from folks who understood and appreciated the significance of what was being attempted with the plaque, others had what could best be described as rather parochial and puritanical comments on this interstellar message.

Most of the people in this second category were upset that the human representations were not only not wearing any clothing, but were subsequently displaying their genitalia – though in the case of the female, this was not entirely true. Even the plaque makers deferred to modesty when it came to that feature in order to ensure that the plaque made it onto the probe at all. A subjective form of moral decency may have been preserved, but the result may one day be further confusion about our species for those who lay their appendages and senses upon the plaque in some undetermined future.

Other plaque complaints included the presumed absence of a particular race for the humans, the seeming passivity of the female, and the symbolic lack of any deities or their religions. Some voiced the concern that would be heard for virtually all such subsequent METI (Messaging to Extraterrestrial Intelligence) efforts: The pulsar diagram and representation of our star system would allow and even invite a hostile ETI to become aware of humanity and know where to find us in order to commit subjugation or even extermination.

Image: The Pioneer exhibit at the Boston Museum of Science, which appeared there from 1973 to 1999. Credit: Donald Bellunduno.

Whether or not there are such dangerous beings in the galaxy, one thing is certain: The physical parameters of the Pioneer probes, which in one regard hamper their detection by just about any ETI, are also their saving grace should such sufficient intelligent dangers exist in the Milky Way. For though the nearly identical vessels will survive for eons in the interstellar void and cover many light years of space during their existences, their small dimensions and a lack of power and signaling activity will also make these probes quite difficult to detect, especially for anyone who is unaware of them in the first place.

Even if the Pioneers are found by an alien species one day, there are also the intellectual hurdles to overcome of the recipient species first noticing the plaque attached to the probe and then understanding its messages. Perhaps these presumed obstacles will be all too obvious and easy to beings that can ply the stars and capture long inactive probes drifting in the cold and dark of deep space, but their minds will almost certainly be alien to ours in many key respects: They may come to certain conclusions about our mechanical “ambassador” and its engraved message which would surprise and perhaps even shock us. Sagan even covered that possibility in The Cosmic Connection with a reprint of some imagined alien reactions from the English humor magazine Punch.

As with the first METI transmitted from the Arecibo Radio Observatory in Puerto Rico several years after the launches of Pioneer 10 and 11 – and which, moving at light speed, would rapidly outpace the robotic explorers – the Pioneer plaques were largely a symbolic gesture, a scientific commemoration of a major achievement in human history. The authors of Pioneer Odyssey – among them Eric Burgess – called the plaques “interstellar/intellectual cave paintings.” Anything else that the plaques would inspire and affect from their present into the far future was considered a bonus.

Once the design was completed and approved, the diagrams were engraved onto a rectangular aluminum plate anodized with gold. The plaque was then bolted onto the antenna struts of the Pioneer with the engraved side facing inward towards the main body of the probe to better protect it from erosion by cosmic dust particles.

Image: Carl Sagan holding a copy of the plaque while standing in front of the Boston Town Hall circa 1973.

A much-too-late thought: Would it have been possible to engrave *both* sides of the plaque with the messages? This could have at least improved the chances for the information to survive in interstellar space until found. Having the message facing away from the craft as well as inward in the direction of any external observers would also increase the likelihood of the plaque being noticed as an item of particular interest addressed directly to the discoverers. In any event, the plaque is there aboard both Pioneers traveling with them into the Milky Way and that is what matters.

The First Firsts

Pioneer 10 was finally lofted into space aboard an Atlas-Centaur rocket from Cape Kennedy in Florida on the evening of March 2, 1972. Just minutes later, Pioneer was moving at a velocity of 32,114 miles per hour, over seven thousand miles per hour faster than any spacecraft before it. Eleven hours later, Pioneer 10 passed the orbit of Earth’s Moon, the same distance which took the manned Apollo missions three whole days to reach. The robotic explorer also became the first NASA spacecraft to operate solely on nuclear electric power, a critical component for future deep space vessels.

Four months after launch, Pioneer 10 became the first probe to fly through the Planetoid Belt between Mars and Jupiter. Despite some concerns about the craft being struck and destroyed by an errant particle in that region of space, Pioneer 10 emerged from the belt in February of 1973 unharmed, effectively removing a perceived barrier to space flight beyond the terrestrial worlds of the Sol system.

Pioneer 10 finally encountered the king of the planets in early December of 1973, returning the first close-up images of Jupiter and some of its Galilean moons and other data while being slung by the incredible mass of the planet itself to 82,000 miles per hour, enough to send the probe on its way out of the Sol system.

Thanks to Pioneer 10 and its sister probe, Pioneer 11, which became the second visitor to the Jovian world one year later and then the first vessel to Saturn in 1979, scientists learned much about these two planets and some of their moons. This was important not only for our understanding of the neighboring gas giants themselves, but for the exoworlds that would be discovered circling other suns in the coming decades. Most of the alien planets we know bear at least some similarities to Jupiter and Saturn in both size and composition. The Pioneers gave us our first look at the kind of realms that their remote mechanical descendants will encounter when the first true interstellar explorers arrive at their destinations.

Exceeding Expectations and Distance

The team that built and controlled Pioneer 10 expected the probe to stop transmitting to Earth not long after it crossed the orbit of the planet Uranus in 1980. Instead both Pioneers continued to be of service to science long after their predicted expiration dates, thanks to their design and the RTGs they derived power from to operate. Among their important achievements was the monitoring of the outer Sol system where, to quote the opening lines from a certain science fiction television series, literally no one had gone before. Among their discoveries was that the solar wind extends far beyond the boundaries of the main planets of our Sol system, much more distant than originally thought.

Image: Pioneer 10 enroute. Credit: Don Davis.

Pioneer 10 even assisted the SETI (Search for Extraterrestrial Intelligence) effort by serving as a favorite test subject for The SETI Institute’s Project Phoenix in the mid-1990s. Utilizing NASA’s Deep Space Network (DSN) of giant radio telescopes scattered across the globe, that team was able to detect the probe’s very faint signal from billions of miles across space. Pioneer 10 gave The SETI Institute confidence that they could detect and interpret an artificial extraterrestrial signal, even a weak transmission buried among the natural noise of the Cosmos.

Eventually the power levels in the RTGs of the Pioneers fell to the point that the mission controllers could no longer conserve enough energy among the remaining operating instruments to keep the probes communicating with Earth. Pioneer 11 faded off first on November 30, 1995, when it was over four billion miles from its point of origin. The probe was so far away that even at the speed of light, the final signals from Pioneer 11 took over six hours to reach Earth.

Pioneer 10 lasted a while longer than its near-twin, transmitting scientific data until April 27, 2002. The final signal was detected on January 23, 2003 at a distance of over 7.5 billion miles.

Where Will They Go?

Pioneer 10 and 11 were flung off in opposite directions due to their encounters with Jupiter and Saturn, respectively. Though neither probes are headed towards the Alpha Centauri system, they will take roughly 100,000 years to reach that distance of just over four light years. While one might a bit more speed for an interstellar probe, the Pioneers were the first to examine the edge of our Sol system, our celestial doorstep into true interstellar space.

They also paved the way for the more sophisticated probes Voyager 1 and 2 and also played a large role in those craft having their own messages to any recipients, the golden Voyager Interstellar Records, whose full story may be read in the 1978 book Murmurs of Earth by the people who made them possible.

Though neither vessel will get more than a few light years to several stars in the relatively early stages of their journeys through the Milky Way, Pioneer 10 is expected to be in the vicinity of the red giant star Aldebaran in about four million years time. Pioneer 11 may visit the star Lambda Aquila four million years from now. Whether any intelligences are circling any of the stars the Pioneers will pass by is essentially irrelevant, for if an ETI is ever to detect and acquire these artifacts of humanity, they will need not only sophisticated interstellar capabilities but a rather advanced detection network and devices to halt the Pioneers’ velocity without damaging or destroying them.

Whoever or whatever does find these historic vessels is some distant epoch, I think the last two paragraphs in the Epilog chapter of Pioneer Odyssey sum up their missions and their futures as humanity’s interstellar ambassadors quite well:

“As an epilog to the Pioneer mission to Jupiter, the plaque is more than a cold message to an alien life form in the most distant future. It signifies an attribute of mankind that in an era when troubles of war, pollution, clashing ideologies, and serious social and supply problems plague them, men can still think beyond themselves and have the vision to send a message through space and time to intelligence on a star system that perhaps has not yet condensed from a galactic nebula.

“The plaque represents at least one intellectual cave painting, a mark of Man, that might survive not only all the caves of Earth, but also the Solar System itself. It is an interstellar stela that shows mankind possesses a spiritual insight beyond the material problems of the age of human emergence.”

This article was originally posted on Centauri Dreams

Of all the probe targets in the outer Solar System, Titan is in many ways the most provocative. Not long ago we looked at two concepts — Titan Mare Explorer (TiME) and AVIATR — that would get instruments back into Titan’s atmosphere and, in the case of TiME, onto one of its northern seas. The allure of this moon is surely what goes on in that atmosphere, a nitrogen brew mixed with methane that generates complex hydrocarbons. We’re learning how these fall on the surface to form patterns of dunes made up of organic material, all of this mediated by a weather cycle that involves seasonal change the Cassini spacecraft has strikingly recorded.

Kathleen Mandt (Southwest Research Institute) has been studying methane in Titan’s atmosphere over time using data both from Cassini and the European Space Agency’s Huygens probe (digression: can it really be seven years since Huygens parachuted down through those orange skies? Good grief…) Mandt’s team is looking at heavy methane — methane that incorporates a carbon-13 atom in place of the more common carbon-12. Heavier methane undergoes chemical reactions at a slower rate, giving scientists a tool for measuring change in Titan’s atmosphere.

Says Mandt:

“Methane’s role on Titan is much like the role of water in the Earth’s climate. First, methane and water are the dominant greenhouse gases on Titan and Earth, respectively, increasing surface temperatures. Second, methane rain falls on the surface of Titan much like water does on Earth. Because Titan is the only other known body with a hydrologic cycle similar to our own, understanding how long methane has been present in Titan’s atmosphere is important for making sense of this unique environment that is so different, yet so much like, our own world.”

Image: This false color composite of Titan, taken during a 2005 Cassini spacecraft flyby, shows both surface features (green) as well as areas high in Titan’s stratosphere where atmospheric methane is absorbing sunlight (red). Southwest Research Institute scientists authored a paper in the Astrophysical Journal, using data from Cassini to predict the age of Titan’s current nitrogen-methane atmosphere. Credit: NASA/JPL/Space Science Institute.

The new work uses data from Cassini’s Ion and Neutral Mass Spectrometer and weighs them against data measured on Titan’s surface by the Huygens Gas Chromatograph Mass Spectrometer. Out of that comes an intriguing read on the atmosphere’s age. Methane should have a short life because it is broken down by sunlight and converted to more complex molecules. But even if methane is being replenished from the interior to match what is happening in the atmosphere, the team finds the current nitrogen-methane atmosphere could be no more than one billion years old. Anything older would have produced a larger methane concentration in both the surface lakes and the atmosphere.

Titan’s smoggy atmosphere, a factory for hydrocarbons, must have formed long after the moon itself. Mandt’s work appears in counterpoint with a paper by Conor Nixon (University of Maryland) and team that uses Cassini data (from its composite infrared spectrometer) to estimate the amount of heavy methane in Titan’s atmosphere. While both papers appeared in the same issue of The Astrophysical Journal, they are able to constrain the age of Titan’s chemistry to different degrees, although the two are in agreement that the methane atmosphere formed long after the moon:

“Under our baseline model assumptions, the methane age is capped at 1.6 billion years, or about a third the age of Titan itself,” says Nixon. “However, if methane is also allowed to escape from the top of the atmosphere, as some previous work has suggested, the age must be much shorter — perhaps only 10 million years — to be compatible with observations.”

Nixon’s team believes that continuous replenishment of methane from an interior source would disrupt its age estimates, but Mandt’s SwRI work — incorporating Cassini’s Ion and Neutral Mass Spectrometer and the Huygens data — puts constraints on the escape of heavy methane from the atmosphere, taking such replenishment into account and still arriving at the one billion year estimate. The papers appear in the context of earlier work that found the last major methane eruption on Titan occurred between 350 million and 1.35 billion years ago, with the age of the current surface estimated at between 200 million and one billion years.

Measuring the isotopic composition of methane is telling us how long Titan’s thick atmosphere has been churning out hydrocarbons, assuming that the methane was produced by a single burst of outgassing at a time when Titan’s interior was being restructured. Our next probes to Titan will need to investigate possible methane replenishment, including methane clathrates, in which a methane molecule exists inside a lattice of ice molecules. Does Titan have an interior ocean that could release methane through the eruption of cryovolcanoes of water and ammonia? There is no shortage of questions as we investigate its atmosphere past and present.

The papers are Mandt et al., “The ¹²C/¹³C Ratio on Titan from Cassini INMS Measurements and Implications for the Evolution of Methane,” Astrophysical Journal 749 (April, 2012), p. 160 (abstract) and Nixon et al., “Isotopic Ratios in Titan’s Methane: Measurements and Modeling,” Astrophysical Journal Vol. 749 (April, 2012), p. 159 (abstract). Neither of these articles is yet available outside the journal’s firewall, so check this SwRI news release, or this one from JPL.

This article was originally posted on Centauri Dreams

By Michael Michaud

The following post is a distinct change of pace for Centauri Dreams, a work of fiction that gets at questions at the heart of SETI. We’ve considered many ideas about interstellar probes that humans may one day launch toward nearby stars. But the reverse could occur: A more advanced technological civilization could send a probe in our direction, particularly after detecting signs of life or technology on a rapidly developing Earth.

Michael Michaud is the author of Contact with Alien Civilizations: Our Hopes and Fears about Encountering Extraterrestrials (Springer, 2007), along with numerous other works including many on space exploration. Michael was a U.S. Foreign Service Officer for 32 years, serving as Counselor for Science, Technology and Environment at the U.S. embassies in Paris and Tokyo, and Director of the State Department’s Office of Advanced Technology. He has also been chairman of working groups at the International Academy of Astronautics on SETI issues. Here he takes us into a scenario that could happen one day. If it did, how would we respond?

Alan guided Esperanza with sensitive fingers, feeling the shifting pressures of the ocean on her keel, watching the stress and easing of her sails. Aiming the big ketch’s bow at Catalina Island, he evened out the yacht’s motion to give his partner the stable platform she needed.

Robin hunched over her instruments. The tall, lanky woman had folded herself into the science cockpit that she and Alan had designed together. She was watching for evidence that warmer Mexican waters were penetrating northward into the cold California current.

“I see some signs,” she told him, “but they are subtle, ambiguous. This isn’t strong enough evidence to convince other scientists.”

Alan suddenly pointed off the starboard bow. “What’s that?”

Robin’s keen blue eyes focused on a metallic object rocking in the waves a quarter mile away. “It’s an automated submersible, part of the ARGO system. There are hundreds of them, all over the world ocean. They sample the chemistry and measure the currents, as far down as three thousand feet.”

“What is it doing on the surface?”

“They’re programmed to come up every ten days to report their findings by satellite.”

“A mind in the waters,” commented Alan.

“Yeah,” said Robin, “but made of silicon.”

They watched the robot doing its job. Its message sent, the machine sank out of sight.

Alan mused aloud. “If you wanted to hide a clandestine undersea vehicle, you would make it look just like that.”

Robin switched off her instruments. “Enough with ocean research for today. I’ve hit the saturation point. Is there something else we can do, just for the hell of it?”

“Have you ever watched a meteor shower?”

“I tried once on Long Island. There was too much urban glow.”

“Tonight we’ll get one of the best of the year. We could anchor off Catalina to watch it.”

“There’s a lot of light on this side of the island, like those camps for religious groups.”

“Then,” said Alan, “we’ll go over to the Dark Side.” Robin groaned, theatrically.

Alan needed her help with the sails as they rounded Catalina’s west end. He and Robin managed the lines together, working as a well-practiced team.

Robin trusted her captain. Alan had reached out when her scientific career stalled, giving her a place aboard as crew for his charter voyages. Stocky but trim, he was warily alert to the ocean’s moods.

Suddenly, Esperanza faced a vast, empty Pacific. Alan and Robin glanced at each other, wordlessly. They had talked of greater voyages, of lonely atolls and distant reefs, where the test and the joy lay in mutual reliance.

They found a deserted cove, dropping their anchor in deep water. After dinner, they lay back on the deck to watch the sky, as dark as it was before electricity.

Far above them, Earth’s atmosphere encountered a swarm of rocks and ice. White streaks emerged from a focal point in the sky. Meteors flashed their brief lives.

“It’s like being the target in a shooting gallery,” said Alan. “I’m glad they burn up before they hit the ground.”

Robin pointed upward. “What about that one? It’s not moving.”

Alan focused on the point of light. It had no tail, no streak of incandescent matter. “Is it my imagination,” he asked, “or is that thing getting brighter?”

“You’re right. It’s coming straight at us!”

Alan tried to be reassuring. “The odds of a meteorite hitting us are infinitesimal.”

Robin’s eyes widened as their fiery visitor grew in size. “We need to take cover!” She dove into the main cockpit, Alan tumbling in after her.

The ocean erupted a mile away, a tower of water bursting upward into the night sky. The sound quickly followed — a crackling whoosh, then a boom that shook the boat.

“Hold on!” Alan shouted. Spray rained down on the huddled sailors. Violent waves rocked Esperanza, straining her anchor chain.

Robin raised her head, watching the restless ocean subside. “That was close!”

“The meteorite may have survived,” said Alan. “Let’s look for it.”

“How?”

“It’ll stay hot for a while. We may be able to spot it through Rover’s infrared sensor.”

They uncovered their remotely operated vehicle, the gadget-loaded undersea craft that extended their reach deep into the ocean. Rover was more than a tool to Alan and Robin. With its own eyes and its own means of locomotion, the ROV had a kind of personhood. It was the closest thing they had to a child of their own.

Alan attached Rover to the yacht’s lifting boom, lowering the machine into the ocean. Robin, at the controls, guided the submersible through the darkness.

They watched the screen intently as Rover neared the point of impact. Nothing but inky blackness.

“Let’s set up a search pattern,” said Alan. “Back and forth, close to the bottom.”

For long minutes, they saw only the dark.

“There!” said Robin, pointing to the edge of the screen. “I see a faint glow on the ocean floor. I’ll send Rover in for a closer look.”

Alan discerned a blurry image, an unearthly shine. “Can’t see any detail.”

“I’m switching to visual,” said Robin. “I’ll turn on the lights.”

She snapped on Rover’s powerful mercury gas lamps. The sudden brightness overwhelmed their vision.

As their eyes adjusted, they made out a dark lump on the ocean floor, lit from within. “It looks like a molten chocolate dessert,” said Alan.

“You would think of that. Hey, do I see something moving?”

“The meteorite is changing shape. They’re not supposed to do that.”

They watched the dark material sliding off the mysterious object, revealing a brighter surface underneath. Robin’s jaw dropped. “It’s shedding!”

“That,” said Alan, “is no meteorite.”

Forgetting to breathe, they watched a glowing crystalline object emerge from the blackness. Robin gasped. “It’s beautiful!”

“Are we seeing internal structure?” asked Alan. “There seem to be patterns, in three dimensions.”

“It keeps changing. It’s like watching a kaleidoscope.”

“Let’s turn on all the detectors. Everything you use for research.”

The hydrophone picked up a soft beeping sound. Alan and Robin listened intently.

“Maybe it’s a tracking signal,” said Alan, “so the people who launched this thing can find it.”

“No, wait. It’s more complex, like a message.”

“As if it were trying to communicate with Rover.”

“One machine to another,” said Robin. “But Rover isn’t smart enough to respond.”

“We are. Let’s signal back.” Alan sent low-power pulses from Esperanza’s directional sonar.

The glowing object silently rose from the seabed, shedding the last of its dark covering.

“It’s oval in shape,” said Alan. “Like a streamlined football.”

“I’ll tell Rover to follow it.”

“Where is it going?”

Robin studied the plot that showed Rover’s location. “Toward us.”

They watched as the visitor approached Esperanza’s steel hull. The glowing machine stopped twenty feet off their bow. Robin maneuvered Rover to a respectful distance, while Alan preserved the scene on video disk.

“I’m receiving a burst of signals,” Robin reported.

“It’s talking to us,” said Alan.

“I’ll record the message.”

“Can you make sense of it?”

“I’ll try the program I use to extract patterns from dolphin signals.”

Alan waited a decent interval, worrying that their visitor would leave. “Any luck?”

“I can’t make out a message,” said Robin. “It’s more like radio noise.”

“Maybe it’s not a language we can understand.”

Robin threw up her hands. “We have to do something, before it gives up on us.”

“Send it the most complicated digital files you have. Even if it doesn’t understand, it will recognize our messages as complex.”

“I have a bunch of oceanographic papers in the computer. I’ll convert them.”

“I’ll try to keep it entertained by turning the lights on and off.”

He watched as the ovoid machine disappeared into the darkness, then returned into the light. Its subtle color changes made his signals seem as mindless as airport beacons.

He introduced patterns, short and long. Would the machine understand an SOS?

Robin finished converting her files, full of words and data in digital form. “Who would find this interesting,” she asked, “except another oceanographer?”

“I love reading your papers,” said Alan.

“Yeah, yeah. When you want to put yourself to sleep.”

“Try sending one.”

They waited in frozen silence. Another burst of signals came from the visitor.

“It worked!” said Alan. “Keep transmitting.”

Robin continued sending her papers. The glowing object beeped politely after each one.

“Where did this thing come from?” she asked. “Could it be some exotic military technology?”

“I would be surprised if any country is this far advanced.”

She stared at him, waiting for his next sentence. He said nothing.

They ran out of files as the dawn began lighting the sky outside the boat. Their visitor remained silent.

“Maybe it’s analyzing,” Robin said hopefully, “digesting our messages.”

“Why do I get the feeling,” asked Alan, “that we’re not telling it anything it doesn’t already know?”

“We can’t keep using the word it,” said Robin. “That thing has a mind. It deserves a name.”

“How about Art, short for artifact?”

Robin shook her head. “Ugly. We’ll call it Artemisia.”

“You just gave it a female gender.”

Robin tilted her nose slightly upward. “It is a more advanced form of life.”

Suddenly, Artemisia began to move.

“Dammit!” cried Robin. “She’s turning away from us. Where is she going?”

Their hydrophone picked up new sounds, the chugging of an engine, the whine of a propeller. “We have company,” said Alan. “Let’s go topside to see who it is.”

He scanned the horizon through his binoculars. There, approaching from the north, was an aged trawler belching smoke.

Alan studied the small, seaworn ship, her sides streaked with rust. “She’s equipped with a crane, like a salvage vessel.”

Robin checked her screen. “Artemisia is sinking back toward the sea floor, disappearing into the dark. Maybe she doesn’t like the noise.”

“Send Rover after her,” said Alan. “I’ll watch the trawler.”

Focusing on the ship’s wheelhouse, he saw a bearded man at the helm. “I bet this guy is a salvager looking for a wreck. There’s a shotgun hanging on a rack behind him. Do we still have a rifle on board?”

“I’ll get it,” said Robin.

“Keep it out of sight until we know what’s going on.”

The trawler slowed to a stop thirty yards away. Alan heard the engine grind into neutral.

The bearded man stepped out of his wheelhouse, speaking through a loud hailer. “I’m looking for a meteorite that hit near here. I tracked it from the mainland. Did you see where it came down?”

“Are you a scientist?” asked Alan.

“Naw, just a collector. I sell them on the Internet.”

“We saw a bright meteor trail,” said Alan. “Something hit the water, but it was farther offshore. Maybe two or three miles.”

Robin, standing in the companionway, watched her partner’s face as the trawler chugged away. “Not like you to shade the truth.”

“He would sell Artemisia to the highest bidder.”

Two miles out, the trawler began tracking back and forth, searching the sea bottom with a towed array of sensors. Alan worried aloud. “What if Artemisia sends signals to him too?”

Robin checked her instruments. “She’s silent, as if she fears the trawler.”

“You’re giving her emotions.”

“Any intelligent being may be wary of strange men.”

“Thanks for implying that I’m not strange.”

“So what do we do? Wait until meteor man is gone?”

Alan studied the trawler’s movements. “His search pattern is bringing him closer to shore. Toward us, as if he suspects our story. We should get under way to draw him off.”

“And hope that he won’t find Artemisia?”

“Let’s ping her with sonar, then begin moving away slowly. Maybe she’ll get the hint.”

Robin sent the briefest ping their sonar could produce. Rover’s screen showed a glow in the dark. “She’s still responding to us.”

Alan nodded. “I’ll start the engine.”

“She doesn’t like engine noise.”

“Ah, yes,” he said. “Females are more sensitive.”

Alan hoisted minimum sails, then raised Esperanza’s anchor. The yacht slowly drifted south, moved as much by the current as by the wind.

“I have to tell Rover to catch up with us,” said Robin.

“I’m sailing as slow as I can,” Alan replied.

Robin watched the video image from the ROV. “Artemisia is rising again. She’s following us.”

Alan deployed the lifting boom to bring Rover back to the yacht’s deck. “Will Artemisia want to come on board too? She may be too heavy.”

“She’s maintaining the same distance.”

Robin set up a program to transmit underwater signals at regular intervals, like a beacon. “I hope this is enough.”

Rounding the east end of Catalina, Alan steered for the California coast. Robin held her breath, hoping that Artemisia too would change course. That mysterious being followed Esperanza like an intelligent dog.

Robin heard Alan’s expelled breath. “You were worried too,” she said.

“Artemisia is a lot more interesting than any machine I ever knew.”

Alan pointed off their beam. “Dolphins, leaping out of the water for the sheer fun of it.”

“I can hear them through the hydrophones,” said Robin. She listened intently. “I’m picking up something new. Artemisia is imitating the dolphins’ squeaks.”

“She’s communicating with them too?”

“She’s turning away from us! She’s following the dolphins!”

“We can’t keep up with dolphins under sail.” Alan reached for the ignition. “The engine will help a little.”

“Yes, yes!” shouted Robin. “I’ll send her every kind of signal I can think of.”

Robin filled the near sea with messages, hoping desperately for a response. The squeaks receded into the ocean’s background noise, now corrupted by Esperanza’s diesel. The dolphins – and Artemisia – were gone.

Esperanza rocked in the waves, until Alan and Robin accepted their loss.

Alan grunted. “It’s humiliating to think that we’re less interesting than dolphins.”

“At least we recorded her signals. Maybe someone can figure out what they mean.”

“We got video, but the quality is not very good.”

“Dammit!” Robin cried. “That was once in a lifetime.”

“Alan spoke gravely. “Maybe once in a millennium.”

“What…” She pointed to the sky. “You think Artemisia came from out there?”

“I know what most scientists would think of that theory. But I can’t come up with a better one.”

Alan and Robin sailed home in sullen silence. They brought Esperanza into her slip, making her fast with docking lines.

“We should clean up the boat,” said Alan. “Shut down all the systems.”

“Not tonight,” said Robin. “I’m too depressed.”

Alan lay in his bunk, trying to read. Nothing held his interest. Nothing matched Artemisia.

What could she have been? An artificial brain, with an impervious shell and an invisible propulsion system?

Some scientists had speculated that humans would be succeeded by intelligent machines. Would they be just sophisticated robots, or could they choose what they would do and where they would go?

Machines could tolerate hardship and boredom far better than a biological being. Would such a sapient entity have feelings?

If Artemisia had stayed longer, he and Robin might have been able to tell. Now she was gone, because they had not been clever enough to hold her interest.

Alan hung a transmitting hydrophone off Esperanza’s stern. Connecting his multi-disk player, he began transmitting music into the deep. He started with Bach’s greatest fugue.

A silly thing to do. Like leaving a porch light on in the hope that your angry lover will return, forgiving everything.

Alan arose early the next morning, letting Robin sleep.

He began washing salt off the boat. As he wiped down the stern rail, he noticed an odd glow in the water. He leaned overboard, staring into the murky darkness.

A smile spread slowly across his sun-damaged face. “Well,” he said, “hello there.”

Robin hugged him as if he had saved her life. Alan shrugged modestly. “Maybe we are more interesting than dolphins.”

“We need to show her that we want to exchange information, to converse.”

“Converse? How?”

“I don’t know yet. I’m running her signals through the best analytical programs I can find. Her language is not like anything I’ve ever seen.”

“Maybe she found dolphin language more recognizable.”

“That could be it!” said Robin. “She may have thought that intelligent life exists only in the sea.”

Alan extended their thought experiment. “She, or whoever sent her, may not have known of humans.”

“How could they miss us? We’re noisy as hell, sending out radio, television, and radar signals.”

“They might have been searching for other forms of life, or other evidence of intelligence.”

“Why would she stick around when we have nothing to offer but scientific junk mail?”

Alan scratched his unshaven chin. “We may be the surprise.”

“I’m running out of things to send her.”

Alan pondered. “You receive television through your computer, right?”

“Everyone does, except you.”

Alan ignored the dig. “How about sending her the news?”

Robin brightened. “It’ll take me a while to program that.”

“What am I going to do to keep her interested in the meantime?”

“Well,” said Robin, “you could sing to her.”

Alan donned his wet suit, slipping into the water beside Artemisia. Hesitantly, he laid his hand on her translucent surface, half expecting a shock. He felt nothing but crystalline hardness.

Her internal glow seemed brighter. Is she responding to me?

Alan sang every song he could remember, making up phrases where he had forgotten the words. How awful this must sound, with the distortion of the watery medium and his own limitations as a singer.

He remembered Robin’s sarcasm. Jailers could use his singing voice on prisoners at Guantanamo Bay. Surely they would confess.

Artemisia beeped. More slowly this time, as if she were adjusting to his inferior intelligence.

He was feeling the first numbness of hypothermia when an object appeared in front of his face mask — the small board that he and Robin used to write notes while they were diving. Robin’s message was brief: “I just started sending her the news.”

Alan was slow to rise to the surface. “Can’t talk,” he croaked. He had given Artemisia everything he had.

Robin helped him to stand. She threw an arm around his waist, bracing him against a fall.

“Let’s watch the news,” she said, “on a real television set.”

The images on Esperanza’s screen seemed even uglier than usual, the commentary even more inane. “This may convince her,” said Robin, “that we really are stupid.”

Alan pointed to the screen. “Navy ships are conducting a search operation off the back side of Catalina.”

Robin studied the steep island slope in the background. “That’s where we were.”

“They’re using a submersible. They’re looking for Artemisia.”

“If Meteor Man talked, the Navy will come to see us. They’ll see the glow. Where can we hide her?

“Maybe we can put something over her, to disguise her.” He paused. “If this is a serious investigation, they may seize your computer.”

“All my work is on that machine!”

“Can you transfer your files?”

“I’ll put them on disks, then overwrite the data. I hope that’s enough.”

Alan grabbed their underwater video camera. “I’ll take close-ups, just in case we lose her.”

The Navy telephoned the next morning, inviting themselves aboard Esperanza at ten.

“Time to hide our visitor,” said Alan. He donned his SCUBA gear, picked up a tarpaulin, and slid quietly into the water.

He hovered over Artemisia’s glowing bulk. “I need to cover you for a few hours,” he told her. He must sound as idiotic as barbarians sounded to the ancient Greeks. Ba ba ba.

As gently as possible, he spread the tarp over Artemisia. He backed off a few feet to watch her reaction.

A gleam penetrated the tarpaulin, turning it translucent. The fabric began to disintegrate, sheets of material falling away. Soon there was nothing left.

I should have known, thought Alan. Don’t imprison intelligence.

Very cautiously, he approached Artemisia again. “I’m sorry,” he said into the water, “but I have to hide you somehow. If I don’t, they’ll take you away.”

He extended his hand toward her, fearing that his flesh would be vaporized. No heat.

He laid both hands on Artemisia’s top. Using his swim fins for leverage, he gently pushed her down. She sank to the bottom without protest.

“Wait here,” he said aloud. “I’ll be back.”

Is it just darker down here, or has her glow diminished?

Robin paced nervously on the pier, wondering what the Navy would do. She imagined armed men brushing her and Alan aside, stripping the yacht, carrying away everything that mattered. They would haul Artemisia out of the bay, dumping her on to a barge. “National security,” they would say.

Too much Hollywood. The Navy had sent only two people, a man and a woman in crisp dress uniforms.

Robin spoke quietly to Alan as the Navy people approached along the pier. “One of us has to lie.”

“And you just nominated me.”

“What if they want to search the boat?”

“We have to let them. If we don’t, they’ll be suspicious.”

“I didn’t have time to clean up my cabin.” Robin studied the neatly dressed female officer. Not a hair out of place.

Captain Babb and Lieutenant MacDonald were attractive officers with excellent posture and keen, penetrating eyes. The Navy had sent its best.

“You must have seen the meteor,” said the firm-jawed Babb.

“Yes,” Alan replied, “we did.” Be responsive, with minimal information.

“It shook us up,” Robin added.

Lieutenant MacDonald focused her bright green eyes on Robin. “You do oceanographic work. Did you search for the object?”

“We looked, but we didn’t find a meteorite.”

Alan intervened. “You might want to ask the man in the trawler. He was equipped to pick up something heavy from the bottom.”

“We did,” said Babb. “He didn’t find it either.”

“I can understand why scientists would be interested in a meteorite,” said Robin, “but why the Navy?”

“It may not have been a meteorite. It may have been a satellite re-entering the atmosphere.”

“One of ours?” asked Alan.

“Can’t say.”

Lieutenant MacDonald smiled at Alan, with fatal charm. “Mind if we look around?”

The Navy people went through every compartment, opening doors and hatches. Robin stayed with them, trying to be cordial.

Alan remained on deck, nervously glancing over Esperanza’s stern. No sign of Artemisia.

As the Navy officers came up from below, he spoke toward the bow. “Everything okay?”

Captain Babb stared into Alan’s eyes. “If you learn anything about this object, can we count on you to tell us?”

“Sure,” Alan responded uncomfortably.

Lieutenant MacDonald smiled, enchantingly. “We’ll be in touch.”

Alan and Robin watched with fixed smiles until the Navy people were out of sight. Alan leaned against a stay, expelling a contained breath. “I hate lying to people.”

“I know,” said Robin, “and so do they.”

Alan returned to the water to raise Artemisia from her hiding place. Robin logged on to her computer to search relevant blogs.

After an hour, she found what she did not want to find. The most credible of the UFO sites reported a rumor that the object striking the sea had not been a meteorite, but some sort of alien craft.

Alan watched over her shoulder as Robin checked other blogs. “This story may spread,” she said.

Alan tried to be reassuring. “It won’t have much credibility.”

“Should we go to the media, tell the real story ourselves?”

“They won’t believe us, unless they see Artemesia with their own eyes.”

“We could give them the video.”

“A mysterious fuzzy light on a dark background? The media have been there before.”

“We can’t keep this to ourselves forever. We don’t have the resources to deal with Artemisia.”

Alan nodded. “At some point, we have to inform the right people.”

“And who might they be?”

“Would scientists do the right thing if they knew?”

Robin spoke sharply. “I wouldn’t count on that. Some of them think they know what’s best for the rest of us.”

Alan tried to step back from his feelings. “We don’t own Artemisia.”

“No one should.”

They stared at the screen as if that would help. The computer offered no wisdom.

“What should we do?” asked Robin. “What should we do?”

——-

Now, dear reader, it’s your turn to suggest the next events in this story. How should it end? What should the discoverers do? Feel free to write an ending of 1000 words or less.

Copyright Michael A.G. Michaud 2007

This article was originally posted on Centauri Dreams

I cannot live without good coffee, and that means fresh beans ground right before brewing, and either manual drip or French press extraction. Every morning after publishing Centauri Dreams I make a couple of cups and go out on the deck to rest my eyes and ponder the state of things before hitting the books for background research in the afternoon. Various thoughts about what to write next always come to me, but yesterday I mused about Enrico Fermi, the legendary Italian physicist who, among so much else, left us with a great unanswered question: Where are they? If it’s so easy for the universe to make intelligent species, why is SETI coming up so short?

Where are they indeed? The day was gorgeous, the air filled with birdsong, temperatures in the mid-60s and a mild breeze. What better setting to be immersed in, thinking about where life emerges and when? I imagined Fermi sitting across from me with a cup of my Costa Rica Tres Rios in his hand, wondering what he might say about the fuss his question has caused over the years. I can almost hear him saying, “Look, it wasn’t serious. It was just a throw-away comment over lunch. I didn’t even think about it.” And then I imagine him gazing out over the hillside and wrinkling his brow. “But you know, it really is an interesting question, isn’t it? I mean, really!”

Image: Enrico Fermi, with no coffee in sight. Credit: AIP Emilio Segrè Visual Archives.

Alpha Centauri: The Age of Things

Obviously I’m putting words in the man’s mouth, but that’s the thing about the Fermi paradox: It keeps coming around. And in one respect it seems particularly disturbing. If the Sun is in the vicinity of stars that are far older than it is, that would give planets around those stars far more time to produce their own living species and far more time for intelligence and technology to emerge. We can think about these things in terms of Alpha Centauri, the subject of these last few posts, because based on recent studies, these stars are much older than our Sun.

How old? To answer the question, the go-to people are Patrick Eggenberger (Observatoire de Genève) and colleagues, who in 2004 produced a paper on the matter that ran in Astronomy & Astrophysics (citation below). A wide range of ages has been posited for these stars over the years, ranging from as little as 2.71 billion years up to well over 6 billion — the paper runs through the previous analyses — but Eggenberger and team go to work with the latest astrometric, photometric, spectroscopic and especially asteroseismic data to reach a strong conclusion: “The global parameters of the α Cen system are now firmly constrained to an age of t = 6.52 ± 0.30 Gyr.”

6.52 billion years, plus or minus 300 million. Now we can think about the Sun’s age, thought to be about 4.57 billion years, and you can see that Alpha Centauri A and B have a 2 billion year jump on us. So does Proxima Centauri, because as we saw yesterday, Greg Laughlin and Jeremy Wertheimer made a convincing case that Proxima is indeed bound to Centauri A and B, and thus probably originated in the same molecular cloud that produced its companions.

I think I’m going to pour Dr. Fermi another cup of coffee about now, because that 2 billion years provides ample time for interesting things to develop given an astrobiologically friendly planet. Long-time Centauri Dreams readers will also know that Charles Lineweaver (Australian National University) has studied the galactic habitable zone and the distribution of stars in the Milky Way by age, finding that 75 percent of the stars in an annular region between 7 and 9 kiloparsecs from galactic center, where life should be possible, are older than the Sun.

Alpha Centauri, using the age estimates of Eggenberger and colleagues, turns out to be fairly average, for Lineweaver says “…the average age of Earths around Sun-like stars is 6.4 ± 0.9 billion years.” He thus thinks that planets around other stars in the galactic habitable zone should be, on average, 1.8 billion years older than our planet, about the same difference as between our Sun and Alpha Centauri. And this is only an average. Milan Ćirković (Astronomical Observatory of Belgrade) notes that there should be inhabited worlds in our galaxy as much as 3 billion years older than our own. So we have on our own doorstep (in astronomical terms) a triple star system that dramatically points to the time frames life has had available to develop civilizations.

Proxima’s Deadly Flares

At this point Dr. Fermi might well take me to task (at least, the imaginary Dr. Fermi who is not only still with us, but completely up to speed on red dwarf studies). I think he would point out that Proxima Centauri is an active flare star with loads of coronal X-ray emission, not exactly a hospitable place for life. We can imagine a calmer, much older Proxima Centauri eventually settling down into a benign middle age, but imagining that also makes us realize that while Alpha Centauri A and B may have provided the opportunity for intelligent life to develop long ago, Proxima may be the most marginal of the Centauri possibilities as of now.

Red dwarfs live, depending on their mass, for trillions of years, so we shouldn’t despair about the future — and we can always ponder whether any kind of adaptive mechanism might rescue astrobiology even in so hostile a place. But as a home for human colonists of the first interstellar mission, any conceivable planet of Proxima Centauri gives way to what we hope to find around Centauri A or B, a rocky world in a habitable zone we might be able to survive within.

Two Charles Lineweaver papers are in play here, the first being “An Estimate of the Age Distribution of Terrestrial Planets in the Universe: Quantifying Metallicity as a Selection Effect,” Icarus 151 (2001), pp. 307-313 (full-text). The second is “The Galactic Habitable Zone and the Age Distribution of Complex Life in the Milky Way,” Science Vol. 303, No. 5654 (January, 2004), pp. 59-62 (abstract). The Eggenberger paper is “Analysis of alpha Centauri AB including seismic constraints,” Astronomy & Astrophysics Volume 417, Number 1 (April I 2004), pp. 235-246 (abstract).

This article was originally posted on Centauri Dreams

You’ll want to bookmark the 100 Year Starship Initiative‘s new site, which just came online. From the mission statement:

100 Year Starship will pursue national and global initiatives, and galvanize public and private leadership and grassroots support, to assure that human travel beyond our solar system and to another star can be a reality within the next century. 100 Year Starship will unreservedly dedicate itself to identifying and pushing the radical leaps in knowledge and technology needed to achieve interstellar flight while pioneering and transforming breakthrough applications to enhance the quality of life on earth. We will actively include the broadest swath of people in understanding, shaping, and implementing our mission.

And check here for news about the 2012 public symposium, which will be held in Houston from September 13-16. Quoting from that page:

This year, 2012, DARPA gave its stamp of approval to and seed funded —100 Year Starship (100YSS)—a private organization to achieve perhaps the most daring initiative ever in space exploration: human travel beyond our solar system to another star!

Meeting the challenge of 100YSS will be as or even more transformative to our global world as Sputnik or DARPA’s commercialization of the ARPA net that became the Internet. Make no mistake; this is not your grandfathers’ space program. 100YSS—An Inclusive, Audacious Journey Transforms Life Here on Earth and Beyond.”

Join us in Houston, September 13-16, 2012 at the 100YSS Public Symposium as the journey begins!

This article was originally posted on Centauri Dreams

Although we haven’t yet found any planets around Proxima Centauri, it would be a tremendous spur to our dreams of future exploration if one turned up in the habitable zone there. That would give us three potential targets within 4.3 light years, with Centauri A and B conceivably the home to interesting worlds of their own. And the issue we started to look at yesterday — whether Proxima Centauri is actually part of the Alpha Centauri system or merely passing through the neighborhood — has a bearing on the planet question, not only in terms of how it might affect the two primary stars, but also because it would tell us something about Proxima’s composition.

A Gravitationally Bound System

Greg Laughlin makes this case in the systemic post I referred to yesterday. It was Laughlin and Jeremy Wertheimer (UCSC) who used data from ESA’s Hipparcos mission to conclude that Proxima was indeed bound to Centauri A and B. Here I want to quote the conclusion of the duo’s paper on the matter, which takes us into some interesting ground indeed:

The availability of Hipparcos data has provided us with the ability to implement a significant improvement over previous studies of the α Cen system. Our results indicate that it is quite likely that Proxima Cen is gravitationally bound to the Cen A-B pair, thus suggesting that they formed together within the same birth aggregate and that the three stars have the same ages and metallicities. As future observations bring increased accuracy to the kinematic measurements, it will likely become more obvious that Proxima Cen is bound to the Cen A-B binary and that Proxima Cen is currently near the apastron of an eccentric orbit…

First of all, the idea of Proxima Centauri as part of a triple star system makes sense given Proxima’s small relative velocity with respect to Centauri A and B (0.53 ± 0.14 km s^-1). The star lies close by the binary pair at 15000 plus or minus 700 AU [and note that I incorrectly posted this distance yesterday, though the error is now corrected to reflect these figures]. Laughlin and Wertheimer calculate that the likelihood of this configuration occurring by chance is less than 10^-6, adding that “ …based on this incredibly improbable arrangement it has been suspected that the stars constitute a bound triple system ever since Proxima’s discovery…”

Note too the implication that Proxima Centauri was born out of the same molecular cloud as its close neighbors, which would imply that all three have the same age and metallicity. Now that’s interesting. We know a lot about Centauri A and B, and in particular we know that both stars are more rich in metals than the Sun, with recent work by Jeff Valenti and Debra Fischer indicating a metallicity of about 150 percent of the Sun’s, and this may be a low-ball estimate, given other recent work on the matter. The link between metals — elements higher than hydrogen and helium — and planets is well established for gas giants and may well extend to small, rocky worlds, as we saw the other day in Falguni Suthar and Christopher McKay’s paper on habitable zones in elliptical galaxies. A metal-rich Proxima Centauri would boost its chances for planets.

Image: Light takes only 4.22 years to reach us from Proxima Centauri. This small red star, captured in the center of the above image, is so faint that it was only discovered in 1915 and is visible only through a telescope. Recent research is revealing much about its composition and the likelihood of planets there. Credit & Copyright: David Malin, UK Schmidt Telescope, DSS, AAO.

If we thought Proxima were not bound by Centauri A and B, we’d have a problem, because as Laughlin noted on systemic, it’s tricky to figure out the metallicity of a solitary red dwarf:

Metallicities for red dwarf stars are notoriously difficult to determine. Low-mass red dwarfs are cool enough so that molecules such as titanium oxide, water, and carbon monoxide are able to form in the stellar atmospheres. The presence of molecules leads to a huge number of lines in the spectra, which destroys the ability to fix a continuum level, and makes abundance determinations very difficult.

But if you have a red dwarf within a multiple star system, you can use the metallicity of the more massive primary star(s) to infer the metallicity of the red dwarf, a method that has produced a metallicity calibration for red dwarfs that thus far has proven useful. All of this means that if Proxima Centauri is indeed bound to Centauri A and B, then its metallicity is on the same order as theirs. When Xavier Bonfils (Observatoire de Grenoble) and colleagues went to work on red dwarf metallicity in 2008, they examined 20 red dwarfs whose metallicity could be estimated in this way. Of those 20 stars, reports Laughlin, only five were higher than the Sun in metallicity, and only one star, GL 324, proved to be as rich in metals as Proxima Centauri.

Proxima Planets: What We Can Exclude

From the standpoint of metals, then, we’d expect the Alpha Centauri stars should have the materials needed for the formation of rocky planets, but what have we observed around Proxima Centauri? The most recent work from Michael Endl (UT-Austin) and Martin Kürster (Max-Planck-Institut für Astronomie) works with seven years of high precision radial velocity data using the UVES spectrograph at the European Southern Observatory. These observations went from March of 2000 to March of 2007 and found no planet of Neptune mass or above exists there out to about 1 AU from the star.

Let’s pause for a moment. These are radial velocity studies about a star the orientation of whose planetary system — if one exists — is unknown to us. If there are planets here, we could be looking at the system from almost any angle, so that any mass calculations have a lot of play in them. Consider a large planet at a high angle to the line of sight. A gas giant like this could cause a radial velocity signature roughly similar to a much smaller planet in a system where the orbital plane was on the line of sight. In other words, the radial velocity technique is insensitive to the reflex velocity in the plane of the sky, giving us only a lower limit to a planet’s mass.

All that is by way of saying that a planet larger than Neptune could conceivably still be there around Proxima Centauri, but the odds do not favor it. We also learn from Endl and Kürster that no super-Earths have been detected larger than about 8.5 Earth masses in orbits with a period of less than 100 days. As for the habitable zone of this star — thought to be 0.022 to 0.054 AU, which corresponds to an orbital period ranging from 3.6 to 13.8 days — we can rule out super-Earths of 2-3 Earth masses in circular orbits. Here we pause again: The authors stress that their mass limits apply only to planets in circular orbits. Planets above these mass thresholds could still exist on eccentric orbits around this star.

So no planets yet around Proxima Centauri, and we’re beginning to rule out entire categories of planet here. We also have the possibility of smaller worlds in interesting orbits. The encouraging thing is that the radial velocity work on Proxima is getting better and better, and the authors see us closing in on planets of Earth size:

With the results from this paper we demonstrate that the discovery of m sin i ≈ 1 M⊕ [one Earth mass] is within our grasp. Since sensitivity is a function of RV [radial velocity] precision, number of measurements and sampling, adding more points to the existing data string in a pseudo-random fashion, will allow us to improve the detection sensitivity over time.

On the broader question of M-dwarf planetary systems in general, Endl and Kürster note the ambiguity inherent in radial velocity studies in terms of mass. One way we can supplement our red dwarf studies is to find low-mass planets inside the habitable zone of such stars, where their close orbits make them more likely to transit the star than planets on wider orbits. Moreover, such transits will be more detectable — we say they have a greater ‘transit depth’ than for other types of star, referring to the change in brightness as the planet transits the star. As we discover transiting super-Earths in close orbits around M-dwarfs, then, we’ll be able to put them on a mass/radius diagram that will help us understand what’s happening around other such stars.

But we’re still not through with Proxima Centauri and its nearby companions. Just how old are these stars? More on that tomorrow, when I’ll consider the question in terms of what’s around us in the stellar neighborhood.

The paper is Endl and Kürster, “Toward Detection of Terrestrial Planets in the Habitable Zone of Our Closest Neighbor: Proxima Centauri,” Astronomy and Astrophysics, Volume 488, Issue 3, 2008, pp.1149-1153 (abstract).

This article was originally posted on Centauri Dreams